Increasingly, test devices in the form of reagent strips are being used to provide convenient and rapid analysis of various types of samples, including liquid samples of biological, industrial and other fluid substances. Diagnostic test devices designed for detecting various clinically significant substances or constituents in body fluids, such as urine and blood, have in many cases supplanted prior wet chemistry techniques which were both cumbersome and time consuming. Diagnostic test devices have assisted in the fast, inexpensive and accurate diagnosis and treatment of disease.
Conventional test devices generally comprise an absorbent or porous matrix incorporated with indicator reagents which produce a detectable result, usually of a colorimetric nature. The sample to be tested is contacted with the matrix, such as by momentary immersion, where the sample is liquid, and an indicator response is observed after a period of time. The response can be observed instrumentally or visually, depending on the particular test device. In the detection of occult blood in urine, for example, a diagnostic test device can be employed which comprises absorbent paper as the matrix impregnated with o-tolidine and peroxide. When this test device is wetted with urine containing occult blood, decomposition of the peroxide occurs with the accompanying oxidation of the o-tolidine to provide a color response. This test is sensitive and extremely useful in diagnosing urinary tract disorders.
For ease in handling, the absorbent or porous matrix, sometimes called a "carrier matrix", is advantageously affixed to one end of an insoluble support member such as an organoplastic strip, e.g., polystyrene, by suitable means such as double faced adhesive tape. Optically transparent substrate material known as Trycite, polystyrene film obtained from Dow Chemical Company, is preferred. The support member normally has a thickness of about 0.19 mm, a width of about 5 mm and a length which can vary depending on the intended use, the number of reagent carrier matrices present, etc. Currently, test devices are being made by the Ames Division of Miles Laboratories, Inc. having lengths of about 85.5 mm and about 82.5 mm. Obviously, based on these dimensions and the materials involved, such test devices tend to be small, elongated and flexible in nature.
Notwithstanding the use of "identical" materials and reagents for the manufacture of test devices, variations occur from one batch to the next and such variations can be significant enough to affect the performance characteristics of a particular test device. Accordingly, test manufacturers have found that it is normally necessary to calibrate instrumentation used in connection with such test devices in order to compensate for variations from lot to lot in the test devices manufactured. In addition, manufacturers have found that it is desirable to code test devices which are to be read by instrumentation with some kind of identification in order to make certain that the test device used for a particular analysis correctly correlates with the instrumentation used to measure or read the test device.
Manufacturers have also sought means for assuring users of test devices that a test device inserted into automated equipment is properly aligned and accurately positioned with respect to the automatic readout means. Misalignment, or misregistration, can result in an improper identification or reading of the test device.
Various techniques have been suggested for encoding information into or on a strip, including application of a magnetizable film (EP No. 132 790 A), the perforation of a strip (U.S. Pat. No. 3,526,480) with a coded pattern, the application of different fluorogens which can be scanned by a fluorescent scanning device (U.S. Pat. No. 3,551,295), and the application of an optical type bar coding (U.S. Pat. No. 4,510,383) for imparting information which can be transmitted to instrumentation.
Optical readers tend to be expensive. Moreover, light radiating means and light sensitive receivers tend to be sensitive to variations in positioning of a test device. The application of a magnetic strip to test devices, on the other hand, has the disadvantage that the magnetic pattern must be scanned to provide useful information, i.e., the coding element must move relative to the reading element; the magnetic pattern is subject to being erased and/or altered due to nearby electrical or magnetic fields such as those from motors, etc.; and the coding of information into a magnetic field and the retrieval of the coded information requires relatively sophisticated and expensive equipment.
In U.S. Pat. No. 3,000,498 graphite based ink is applied to the rear surface of a postal stamp in portions where the stamp is strongly colored or heavily printed. The printing is invisible to the naked eye but detectable by sensors moving across the stamp to determine the value of the stamp.
In U.S. Pat. No. 4,230,938 electrosensitive material is applied to checks, business forms and the like in the form of bar codes of horizontal synchronization marks or vertical synchronization marks or timing tracks which can be sensed by moving a sensor over the forms.
The present invention has been developed for the purpose of providing an improved system for the identification of test devices as well as the calibration of instrumentation used with such test devices. In addition, the system which has been developed can be used for the purpose of assuring proper alignment between a test device and instrumentation.